The present invention relates generally to an improved apparatus for trimming the open end of a container prior to being sealed, and more particularly to trimming the open end of aluminum beverage can bodies after the can bodies have been drawn and ironed.
The invention relates to an improved apparatus for trimming the uneven surface of an end of aluminum can bodies after the can bodies have been drawn and ironed. Aluminum cans are manufactured from flat sheets of aluminum, which are initially formed into small cups that are much shorter and have a larger diameter than typical finished aluminum cans, such as twelve ounce beverage cans available in the retail market today. The cup is further processed by drawing and ironing, to elongate it into a full can body and reduce the diameter. This process produces an irregular surface of uneven height around the circumference of the open end of the can body. This irregular open end can create problems in further processing of the can. For instance, the can may be rejected at a later step of processing called xe2x80x9cthe neckerxe2x80x9d for being out of specification, or if it passes through the necker and is filled and sealed with a lid, the seal may be defective due to the irregular surface at the open end of the can, which may lead to failure of the can.
One way of reducing the likelihood of the can being rejected at xe2x80x9cthe neckerxe2x80x9d or resulting in failure due to an inadequate seal caused by this irregular surface, is to trim the open end of the can prior to further processing. Typically, a rotary can trimmer is incorporated into the production line downline from the can body maker equipment. After exiting the body maker, can bodies are typically loaded into an infeed chute that places the can bodies into a star wheel, which feeds the cans to the trimmer. As the cans rotate around the star wheel, they reach the trimmer cartridge one at a time. Prior art trimmer cartridges such as the rotary can trimmer available from Belvac Production Machinery typically include a pair of substantially parallel rotating blades or knives that open and close to allow the can body to be placed in position for trimming and to be removed after trimming is complete. Prior art blades are spaced apart by gap of about 0.0010xc2x10.0002 inches, in a direction perpendicular to the opening and closing direction. The blades typically overlap in the vertical direction when in a closed position to shear the irregular surface from the top of the can body.
Once a can body reaches the trimmer cartridge of the prior art, it is typically held by a vacuum in a horizontal position or a position perpendicular to the opening and closing direction of the blades with the open end of the can toward the blades, placed so that one blade is inside the can body and the other blade is outside the can body. With the blades closed, the can body is then rotated to cause the blades to trim the entire circumference of the can. After trimming is complete, the can body is removed from the trimmer cartridge and discharged through a chute for further processing, such as cleaning, printing, and necking. The trimmed waste piece is discarded away from the trimmer.
Prior art trimmer cartridges have several problematic features. One problem caused by the size of the gap between the blades in the prior art is that the can body may be left with burrs or a jagged edge, particularly at the stop/start point in trimming. A burr or jagged edge at the top of the can body may result in rejection of the can body at downline equipment or result in a defective seal, which are the types of problems that trimming is designed to overcome. Also, the gap between the blades in prior art trimmers is usually only adjustable from inside the housing, requiring the cartridge to be removed to make an adjustment in the gap. The gap is also typically set using shims, which are more likely to be inaccurate or cause fluctuations in the gap during operation.
Additionally, the housing of prior art trimmers, such as the Belvac trimmer, is usually not sealed to hold in lubricant and keep out contaminants. Aluminum shavings and body coolant are possible contaminants that can enter the equipment in a non-sealed system, resulting in more down time for cleaning and repair.
Another drawback of prior art trimmers, such as the Belvac trimmer, is found in the tang, which connects the trimmer cartridge housing to the trimmer equipment and provides rotational power to the trimmer cartridge. Tangs are typically square or octagonal, designed to fit in a corresponding opening in the trimmer machine to be rotated and in turn to rotate one of the trimmer cartridge shafts. The rotation on the tang can cause the edges of the tang to be worn or rounded, requiring the tang to be replaced. Usually, a prior art tang is an integral part of the trimmer housing or an integral part of a blade shaft located within the housing. When it is necessary to replace or perform maintenance on the tang, prior art trimmer cartridges have to be opened, and typically the entire tang and shaft have to be replaced. This increases the downtime required to make the replacement or perform the maintenance, which ultimately increases the expense involved.
Still another problematic feature of prior art trimmer cartridges is the use of helical gears. Although helical gears have their advantages, they also have their disadvantages. The primary disadvantage associated with helical gears is that the angle of their teeth creates a thrust load on the shafts on which the gears are mounted, which must be carried by bearings. A further drawback of prior art trimmer cartridges relates to the shafts on which the blades are mounted. The use of helical gears, which create thrust on the shafts that rotate the blades is another problematic feature of prior art trimmers. Typically, these shafts are not the same size and consequently are of unequal mass. Temperature changes in the trimmer cartridge will cause unequal thermal variations in the shafts because of the mass differential. These thermal variations create fluctuations in the spacing of the blades, which can result in inconsistent or inadequate trimming of the cans.
The present invention provides an improved apparatus for trimming the irregular surface of the open end of an aluminum can after the can has been drawn and ironed. This invention may also be used to trim other types of metal containers, but is preferably used for aluminum beverage cans.
A preferred embodiment of the disclosed trimmer apparatus includes two rotating blades to cut the top edge of the can. These blades are preferably substantially parallel to each other. Other embodiments may be used according to the invention, including an embodiment where only one blade is used in combination with a rigid or semi-rigid cutting surface for the single blade to cut against. In a preferred embodiment, a rotating stationary blade is mounted on a shaft that does not allow horizontal or vertical movement of the stationary blade and a rotating pivoting blade is mounted on a shaft contained in an inner housing that allows both horizontal and vertical movement of the pivoting blade. Other configurations, such as where both blade shafts are capable of horizontal or vertical movement, or where one shaft is capable of horizontal movement and the other capable of vertical movement, may be used and are within the scope of the invention.
Another feature of a preferred embodiment of the trimmer apparatus is that the pivoting blade moves in a direction, most preferably in a vertical direction, to cause the blades to open and close around a can body being trimmed. Preferably, the pivoting blade is mounted on a pivoting blade shaft partially contained in an inner housing of the trimmer cartridge. The entire inner housing, including the pivoting blade shaft, the pivoting blade, an adjustment shaft, and bearings, move vertically to open and close the blades. The open position allows placement of a can body to be trimmed and ejection of the can body once trimming is complete. Trimming takes place while the blades are in the closed position.
The blades preferably overlap while in the closed position, resulting in a fixed cut width of about 0.156 inches. Trimmer cartridges in the prior art, such as the Belvac trimmer, have cut widths that are adjustable, which typically results in variations in the cut. A fixed cut width results in more standardized cuts with fewer occurrences of burrs or other irregularities in the cut end of the trimmed can.
An additional feature of a preferred embodiment of the trimmer apparatus is that the two blades are spaced apart in a direction substantially perpendicular to the opening and closing direction by a gap that is between about 8-25% of the metal thickness of the can, and most preferably between about 8-15% of the metal thickness of the can. In a preferred embodiment, this gap is adjustable by an adjustment mechanism, including an adjustment nut and an adjustment screw, accessible from the exterior of the trimmer apparatus, although other adjustment mechanisms may be used according to the invention. As will be understood by those skilled in the art, and as described in more detail below, the adjustment mechanism causes the inner housing, which contains a portion of the pivoting blade shaft to move in this perpendicular direction, which is typically horizontal, to change the width of the gap between the two blades.
Another feature of the invention is that the gear housing of the trimmer apparatus is sealed with sealing mechanisms, with o-rings being the preferred embodiment of sealing mechanism. The sealed housing prevents contamination, such as metal shavings and body coolant, from entering or building up inside the housing, which may lead to malfunction of the trimmer apparatus and hinder the rotation and movement the of the shafts on the interior of the housing. Reduction of contaminants reduces the amount of downtime needed to clean and repair the trimmer apparatus. Additionally, the sealed housing maintains an adequate lubrication for the moving parts contained therein. Although it is preferred that the housing of the trimmer apparatus be sealed, an unsealed housing may be used according to the invention.
Still another feature of a preferred embodiment of the invention is that the mass of the stationary blade shaft is substantially equal to the mass of the pivoting blade shaft. The use of shafts of equal, or near equal, mass reduces the amount of thermal variation between the two shafts, as the impact of temperature fluctuations will be substantially the same. It is preferred to reduce as many variables in the trimmer apparatus as possible, including those created by thermal variations, to avoid variations in the cut width and the gap between the blades during operation. Shafts of unequal mass may also be used within the scope of the invention.
Another preferred feature of the invention is the use of a tang accessible from the exterior of the trimmer cartridge housing and extending through the housing to connect to and rotate one of the shafts, preferably the stationary shaft. The tang is preferably removable without requiring the cartridge housing to be opened and without requiring removal of the shaft that it rotates. This permits easier and faster replacement of the tang when necessary. Additionally, a tang of the preferred embodiment of the invention is square or octagonal. Although it is preferred to use a square or octagonal tang that is replaceable without opening the housing and without also having to replace the shaft, other tang configurations may be used according to the invention.
Still another feature of a preferred embodiment of the invention is the use of spur gears. Preferably, four spur gears are used in combination with four shafts, including the two shafts on which the blades are mounted, a third, idler shaft that is part of the mechanism to adjust the gap between the two blades, and another idler shaft. The use of spur gears reduces the amount of thrust on the shafts, which also reduces fluctuations in the cut and gap widths between the blades. Other types of gears may be used according to the invention, but spur gears are preferred.
A final feature of a preferred embodiment of the invention is the use of a motion translator mechanism that translates motion to a direction that is substantially perpendicular to a motion translator shaft. This motion translator causes the opening and closing movement of the inner housing, pivoting blade shaft, adjustment shaft, and pivoting blade to open and close the blades. Further, the opening and closing movement occurs while maintaining the pivoting blade in a plane substantially parallel to the stationary blade so that the gap between the blades remains substantially the same during the translation movement.
These features, described in detail below, may be used singularly or combined to trim cans with decreased variation in the resulting trimmed edge. The use of the trimmer apparatus of the invention may also decrease the amount of downtime in the can-making process necessary for repair or replacement of various parts of the apparatus and decrease the frequency with which cans are rejected in processing down line from the trimmer and the frequency of failure in sealed cans due to irregularities in the trimmed edge.